The present invention is related to disc drive data storage systems and, more particularly, to a method of controlling curvature of a transducing head, such as a hydrodynamic bearing slider.
A typical disc drive includes one or more rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective head gimbal assemblies (HGAs). Head gimbal assemblies carry transducers which write information to and read information from the disc surface. An actuator mechanism moves the head gimbal assemblies from track to track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a load beam for each head gimbal assembly. The load beam provides a preload force which urges the head gimbal assembly toward the disc surface.
The head gimbal assembly includes a gimbal and a slider. The gimbal is positioned between the slider and the load beam to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc. The slider includes a slider body having a bearing surface, such as an air bearing surface, which faces the disc surface. As the disc rotates, the air pressure between the disc and the air bearing surface increases, which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. The preload force supplied by the load beam counteracts the hydrodynamic lifting force. The preload force and the hydrodynamic lifting force reach an equilibrium which determines the fly height of the slider. The transducer is typically mounted at or near the trailing edge of the slider.
In some applications, the slider flies in close proximity to the surface of the disc. This type of slider is known as a xe2x80x9cpseudo-contactxe2x80x9d slider, since the bearing surface of the slider can occasionally contact the surface roughness of the disc. In other applications, the slider is designed to remain in direct contact with the disc surface with substantially no air bearing. These sliders are referred to as xe2x80x9ccontact recordingxe2x80x9d sliders.
It is often desirable to fabricate a slider such that the bearing surface has a positive curvature along the length and width of the slider. Length curvature is known as crown curvature. Width curvature is known as cross or camber curvature. The proper setting and control of crown and cross curvature improves fly height variability over varying conditions, improves wear on the slider and the disc surface, and improves takeoff performance by reducing stiction between the slider and the disc surface. In addition, the slider preferably has no twist about its longitudinal or transverse axes. While twist does not directly effect fly height, high twist values, either positive or negative, can cause other negative tribological effects, such as increasing wear and inducing roll.
In a typical slider fabrication process, curvature is controlled by lapping the bearing surface on a spherically-shaped lapping surface or on a flat lapping surface while rocking the slider body back and forth in the direction of the desired curvature. The amount of curvature is determined by the radius of the rocking rotation. This lapping process is difficult to control and results in large manufacturing tolerances. More efficient and controllable methods of effecting air bearing surface curvature are desired.
U.S. Pat. No. 5,442,850 discloses a method of controlling crown and cross curvature by inducing a preselected amount of compressive stress within a selected section of the bearing surface by impinging the section with particles for a preselected amount of time. U.S. Pat. No. 5,266,769 discloses a process of controlling slider crown and cross curvature in which the air bearing surfaces are first patterned and then a chosen pattern of stress is produced on the back side of the slider by laser oblation or sand blasting to selectively remove stressed material and thereby create a desired crown and cross curvature of the bearing surface.
U.S. Pat. No. 4,910,621 discloses a method of producing crown and cross curvature in a slider by creating a groove in the leading edge of the slider, placing a sealing material in the groove and then melting and stiffening the sealing material in the groove. The sealing material has an adhesive property upon melting and a shrinking property upon stiffening which causes lengthwise curvature at the leading edge of the slider. U.S. Pat. No. 5,220,471 discloses a slider having a longitudinal linear groove formed in a surface which is opposite the disc-opposing surface. The groove creates tensile stresses which cause the disc-opposing surface of the slider to be a curved surface in a convex form.
U.S. Pat. No. 5,982,583 discloses a method of effecting slider curvature through the application of laser-induced anisotropic tensile stress, which allows one of the crown and cross curvature to be changed to a greater extent than the other curvature. In addition, Seagate Technology, Inc. has used a process of creating scratches on the back side of the slider (the side opposite to the air bearing), lapping the bearing surface flat and then laser heat treating the scratches to reduce compressive stress caused by the scratches and thereby cause a positive curvature change in the bearing surface. This process is discussed in U.S. application Ser. No. 08/662,849, Filed Jun. 12, 1996 now U.S. Pat. No. 6,078,337.
One aspect of the present invention relates to a method of controlling twist curvature of a disc head slider having a bearing surface, a back surface, which is opposite to the bearing surface, a longitudinal axis and a transverse axis. The method includes obtaining a measure of the twist curvature of the bearing surface and selectively altering material stresses in a working surface of the slider. The material stresses are altered asymmetrically with respect to the longitudinal axis and the transverse axis based on the measure of the twist curvature to induce a change in the twist curvature. The working surface includes the bearing surface or the back surface.
Another aspect of the present invention relates to an apparatus for adjusting twist of a disc head slider having a bearing surface, a back surface, which is opposite to the bearing surface, a longitudinal axis and a transverse axis. The apparatus includes a light source, which is adapted to produce a light beam capable of altering material stresses in a working surface of the slider. The working surface includes the bearing surface or the back surface. The twist of the bearing surface is measured, and a scanner scans the light beam across the working surface in a pattern selected to alter material stresses in the working surface asymmetrically with respect to the longitudinal axis and the transverse axis based on the measure of the twist curvature so as to induce a change in the twist.